rainmeter-studio/RainmeterEditor/UI/SkinsPanel.xaml

<UserControl x:Class="RainmeterEditor.UI.SkinsPanel"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <TreeView>
            <TreeViewItem Header="Sample item">
                <TreeViewItem Header="Sample subitem" />
            </TreeViewItem>
            <TreeViewItem Header="Sample item 2" />
        </TreeView>
    </Grid>
</UserControl>